 IVES 9 IVES Conference Series 9 Measuring elemental sulfur in grape juice in relation to varietal thiol formation in Sauvignon blanc wines.

Measuring elemental sulfur in grape juice in relation to varietal thiol formation in Sauvignon blanc wines.

Abstract

Aim: Sauvignon blanc displays a range of styles that can include prominent tropical and passionfruit aromas. Both sensory evaluation and chemical analysis have confirmed the above-average presence of ‘varietal thiols’ in the Sauvignon blanc wines from Marlborough, New Zealand.1 The varietal thiols are released from cleavage of non-volatile sulfur-containing precursors or an interaction between a sulfur donor and a C6-compound.2 Machine-harvesting is the most common harvesting practice used in New Zealand, by which, there is a higher probability to add some leaves to the must. Leaves and grapes can contain elemental sulfur (S0), which is commonly sprayed in the fields to protect berries against powdery mildew. S0 is known to cause unwanted reductive aromas, including H2S, in certain wines unless remediation steps are undertaken during winemaking. Also, it was shown that extra S0 addition to the crushed grapes could lead to more varietal thiol formation in wines.3 Despite the clear effects of residual S0 present in the must on the final wine quality and aroma4, its measurement is not a regular practice undertaken in wineries due to the lack of easy and applicable methods.

Methods: We have optimized a sulfide sensor for S0 measurement in grape juice samples and investigated the correlation between S0 concentration in grape juice and varietal thiols concentration in final wines. A simple apparatus was designed to reduce S0 to sulfide using dithiothreitol (under acidic conditions, as H2S), followed by an ion-selective electrode (ISE) to measure sulfide concentrations (under alkaline conditions as S2-). GC-MS is being used to analyze thiol concentrations in wine samples to allow comparisons to be made with juice S0 concentrations.

Results: The semi-log calibration curve plotted based on the ISE data showed very good linearity. The results also showed that the reduction process was successful, and the apparatus is working well with both standard and juice samples. The ISE was confirmed to be able to detect the reduced sulfur at concentrations as low as 0.01 ppm.

Conclusion

The methodology allows action between the concentration of S0 residues and the concentration of varietal thiols in the final wines to be investigated. The analysis is applicable in a winery setting to evaluate the potential of grape juices to form varietal thiols and/or reductive compounds in wines

DOI:

Publication date: September 7, 2021

Issue: Macrowine 2021

Type: Article

Authors

Bahareh Sarmadi

School of Chemical Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand,Paul A. Kilmartin, School of Chemical Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand Brandt P. Bastow, School of Chemical Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand

Contact the author

Keywords

Sauvignon blanc, elemental sulfur, varietal thiols

Citation

The generation of suspended cell wall material may limit the effect of ultrasound in some varieties

The disruptive effect exerted by high-power ultrasound (US) on plant cell walls, natural barriers to the diffusion of compounds of interest during the maceration of red wines, is established as the reason behind the chromatic improvement that its treatment causes. However, sometimes this improvement is not observed, especially with short maceration times. The presence of a high quantity of suspended cell wall material, which formation is favored by the sonication, could be the cause of this lack of positive results since this cell wall material has a high affinity for phenolic compounds.

Vineyard management for environment valorisation

[lwp_divi_breadcrumbs home_text="IVES" use_before_icon="on" before_icon="||divi||400" module_id="publication-ariane" _builder_version="4.19.4" _module_preset="default" module_text_align="center" module_font_size="16px" text_orientation="center"...

Vinhos de talha: to pitch or not to pitch

In Alentejo, south of Portugal there is a traditional way of fermenting wines in clay vessels, known as “Vinhos de Talha”. Clay vessels were traditionally impermeabilized using pine pitch, creating a barrier between the fermenting must and the clay. Due to this unusual production technology that uses of clay vessels, instead of inox or wood vessels, “Vinhos de Talha” present unique characteristics increasingly appreciated by national and international consumers when compared with wine obtained by the said traditional methods of winemaking. Although the positive consumers feedback, there is little literature about the physical-chemical characteristics of these wines (Martins et al, 2018; Cabrita et al, 2018). This work aims to characterize the volatile composition of white wines produced in clay vessels with different coatings and to contribute to the knowledge and preservation of these wines that are a unique cultural heritage. Wine samples were produced during 2019 vintage from white grapes, using the traditional technology associated to these wines.

Effect of biological control agents on grapevine rhizosphere microbiome and grapevine defenses

Plant diseases are a major obstacle to crop production. The main approaches to battle plant diseases, consist of synthetic chemicals to attack infecting pathogens. However, concerns are increasing about the effects of chemicals in the environment, leading to an increase in the use of biocontrol agents (BCAs), due to their assets, such as, antagonism, and competition. In this study, we tested the hypothesis that the introduction of Bacillus subtilis PTA-271 (Bs PTA-271) and Trichoderma atroviride SC1 (Ta SC1) produce distinctive modifications in the composition and network structure of the grapevine rhizosphere microbial community, as well as grapevine induced defenses.

Haplotype-Resolved genome assembly of the Microvine

Developing a tractable genetic engineering and gene editing system is an essential tool for grapevine. We initiated a plant transformation and biotechnology program at Oregon State University using the grape microvine system (V. vinifera) in 2018 to interrogate gene-to-trait relationships using traditional genetic engineering and gene editing. The microvine model is also used for nanomaterial-assisted RNP, DNA, and RNA delivery. Most reference genomes and annotations for grapevine are collapsed assemblies of homologous chromosomes and do not represent the specific microvine cultivar ‘043023V004’ under study at our institution.